The present invention relates to a composition and a method for tissue augmentation.
Tissue augmentation is desirable for both therapeutical and cosmetical purposes. A therapeutical application is, for example, augmentation of tissues that need to be enlarged for proper function. Examples of such are the vocal cords, the oesophagus, various sphinters that have become weakened or have too thin tissue mass. Another set of examples are enlargement of the muscles of, for instance, the urether and rectum. In the field of cosmetic surgery tissue augmentation is applied to wrinkles and scars as well as to enlarge lips or fill out age related diminished fat deposits around the eyes as well as other applications. In the cosmetical field, plastic surgeons fill out, for example, eye wrinkles, by injecting tissue augmenting materials.
Materials used for augmentation of tissues are, for instance, the patients own fat cell cartilage or other suitable materials. Commercially available biologically degradable materials include collagen suspensions and crosslinked hyaluronic acid. Non degradable materials include silicone oil, silicone microparticles, Teflon.RTM. paste and other inert materials.
U.S. Pat. No. 5,007,940 teaches the use of deformable, nonbiodegradable hydrogels with a lubricious surface. The patent concerns injecting of nonbiodegradable material which appears by the finding of such material in the brain tissues. Thus any material injected into tissues has a risk of being carried away by the venous blood to central parts of the body. For individuals with a life expectancy of several years this is not likely to be accepted by regulatory authorities. Therefore, such materials are presently not widely used due to migration to critical tissues or long term negative reactions on the health like autoimmune diseases or cancer.
Homotransplantation of tissue is a cumbersome and painful procedure that has a too short action. The most frequently used material today is collagen suspension. However it is made from bovine collagen and can carry unwanted slow action viruses. Most negative is the fact that some patients develop a sensitivity towards the material or get stimulated enzymatic activity in the skin due to repeated foreign body reactions. Despite these drawbacks the products are still very popular. An interesting new product under clinical evaluation is a crosslinked form of hyaluronic acid.
U.S. Pat. No. 5,143,724 teaches the use of viscoelastic gel slurries of high biocompatibility. The patent relates to materials based on hyaluronic acid or s.c. hylans with very low cell interaction which is very useful in some applications but which has a limited value in tissue augmentation uses. The reason is because these materials will spread out in the tissue and loose it's augmenting property.
From the above it appears that the existing materials are clearly not ideal end the search for new improved materials for tissue augmentation continues with the aim to identify materials that are biocompatible, injectable through thin needles, non health threatening and has a residence time in tissues--short enough to disappear when their function is no longer desirable but long enough to be worth the effort to make the implantation.
The present invention addresses this aspect as well as that of versatility in designing an ideal composition for a specific tissue that needs to be augmented. In addition, these same compositions have proven to be very useful vehicles for the delivery of drugs.